The present invention relates to an electromagnet or, more particularly, to an electromagnet which is characterized by the greatly decreased noise when the movable iron core hits the fixed iron core by being attracted thereby and by the uniformity of the ampere-turn required for holding the movable iron core attracted on the fixed iron core.
As is illustrated in FIG. 9 of the accompanying drawing, a conventional electromagnet is typically constructed of the parts including a yoke 1, a fixed iron core 2 fixed relative to the yoke 1, a movable iron core 4 which is attracted by and coming apart from the fixed iron core 2 and a coiled wire 3 wound around the magnetic path formed of the yoke 1, fixed iron core 2 and movable iron core 4 which serves to attract the movable iron core 4 toward the fixed iron core 2 by means of the magnetic flux 5 induced by passing an electric current therethrough.
When the coil 3 is energized and movable iron core 4 is attracted toward and hits the fixed iron core 2, a sharp noise is unavoidably caused more or less by the bumping of the two metal-made parts. This noise generation can sometimes be a serious problem, especially, when the electromagnet is built in a household electric appliance. A conventional measure undertaken to reduce the noise generation in the electromagnet is to provide a covering member 6 made of an elastic material such as rubbers and plastics on the end surface 2a of the fixed iron core 2 or on the end surface 4a of the movable iron core 4.
Such an electromagnet having an elastic covering member 6 on the end surface of the fixed iron core 2 or movable iron core 4 has several problems. For example, the elastic covering member 6 made of a non-magnetic material such as rubbers is provied across the path of the magnetic flux 5 so that the permeance is decreased consequently resulting in a decrease of the attracting force. Since the elastic covering member 6 is repeatedly bumped directly by the fixed iron core 2 or movable iron core 4 made of a magnetic material, the elastic covering member 6 is unavoidably worn out in the long run to produce dusts so that the attracting behavior of the electromagnet is degraded with a decrease in the serviceable life of the electromagnet. Moreover, the noise-suppressing effect and the value of ampere-turn required for obtaining a desired attracting force are not always reproducible when a large number of electromagnets are mass-produced.